This invention relates to printed sound and, more particularly, to a system for generating audible information from indicia printed on paper.
Attempts have heretofore been made to produce a commercially viable "talking book" which would offer the reader, typically a child, audible guidance concerning pictures and words presented on a printed page. The potential educational and amusement advantages of combined audio/visual presentation from a book are well documented. However, previously suggested techniques have not been commercially accepted primarily because of the expense of providing an acceptable audio recording media in book or sheet form and less than satisfactory intelligibility of the sounds reproduced from the recording media with a transducer of modest cost.
Commonly assigned U.S. Pat. No. 3,970,803 granted July 20, 1976 to George R. Kinzie Jr. and Daniel A. Gravereaux, describes a system for generating audible information from indicia printed on paper which can be printed in ink by conventional printing techniques. A sound track printed on the paper is oriented in a manual scanning direction, this being the horizontal direction in most cases, the track consisting of a multiplicity of straight, closely parallel-spaced sound track segments of the variable-area type oriented in a direction generally transverse the manual scanning direction. The segments are arranged in an order which represents sequential portions of the complete sound information contained in the track, with adjacent segments having a substantial degree of waveform redundancy. The sound tracks are printed on the pages of a book, for example, in association with sentences of printed text to which the sound information contained in the printed sound tracks corresponds.
The "folded" printed sound track is transduced with an optical scanner adapted to be manually moved along the sound track in the manual scanning direction, the scanner including mechanical and optical means which automatically scan the track in a direction transverse the manual scanning direction, namely, along the length direction of the sound track segments. The segments are scanned longitudinally at a rate to obtain a signal of desired amplitude and pitch, which rate is not significantly dependent on the manual scanning rate, so the frequencies of individual sound elements are relatively insensitive to changes in the manual scanning rate.
The patented scanning apparatus includes a housing having a smooth bottom surface adapted to rest on the paper over the sound track, the bottom having a transparent opening through which an area of the sound track is illuminated by a lamp mounted within the housing. An opaque enclosure, mounted above the transparent opening, has a narrow, elongated window confronting the transparent opening, and a photodetector supported in the enclosure receives light entering the window and converts it to a sound-representing signal. A toothed wheel supported for rotation about a vertical axis is positioned between the transparent opening and the window, the teeth (six in the disclosed embodiment) being so proportioned that a given tooth completely tranverses the window and masks a portion thereof before the next-appearing tooth begins to traverse the window. That is, the teeth are spaced such that only a single tooth area at a time masks the window, and a new tooth begins traversal of the window just as the previous tooth is completing its traversal. In this type of scan, the average amount of light viewed by the photo-detector through the window (in the absence of the scanning tooth) is a constant reference which is a function of the window width, and variations in the amount of light "blocked out" by the scanning tooth at any instant represents the varying audio signal.
While this prior art scanner produces generally acceptable sound signals, because the sound track segments are straight and the toothed scanning wheel has a relatively small diameter, effects occur which deleteriously affect the intelligibility of the reproduced sound, one being the introduction of phase modulation of the signal from tooth to tooth; this phase modulation and other distortions would be minimal if the tracks were scanned with a very large diameter wheel. Another problem, due to the window being sufficiently wide as to encompass and thus play back as many as two or three adjacent segments simultaneously, is the occurrence of nulls at certain frequencies related to the scanning frequency, manifested as echoes in the reproduced sound signal. Additionally, the frequency response of the scanner is dependent on the physical width of the scanning tooth that traverses the window; if the tooth is relatively wide, as it needs to be from a structural viewpoint, the response of the system to high frequency components in the sound information is less than desirable. Although the frequency response could be improved by narrowing the tooth and thus the width of the scanning slit, the improvement would be at the expense of system gain because of the resulting reduction in the effective area of the scanning slit, and, as a consequence, the variations in the light reaching the photodetector.
A disclosed alternative to the toothed wheel is a circular disk having a multiplicity of radially extending rectangular apertures whereby only a small portion of the track segment is viewed (rather than blocked out) at a time. A scanner with this type of scanning wheel, because of its relatively small diameter and the straight sound tract segments, exhibits the same kinds of problems as those introduced by a toothed scanning wheel.